[App_rpt-users] CM119 USB interface

Brian G gravesb at gmail.com
Mon Dec 24 02:58:51 EST 2018


Hi Kevin, thanks very much... I understand 999 is supposed to represent a
strong fully quiet signal. That's the issue, there isn't one...but app_rpt
thinks there's a signal present and is sending it 100% of the time, unless
I use CTCSS decode (or plain vox), which I don't want to do for this node.

I'm using the discriminator output from a Motorola Radius M120, but the
same issue occurs on other rigs, and the "signal level" is still at 999
regardless of if there's a radio connected to the dongle or not :( If
there's no input, signal level should be at (or close to) zero, shouldn't
it?



On Sun, Dec 23, 2018 at 9:29 PM Kevin Custer <kuggie at kuggie.com> wrote:

> Brian,
>
> If the application reports 999, my guess is you aren't inputting raw
> discriminator audio into the interface.  If the audio you are inputting
> into your radio interface has been Low Pass Filtered or is squelch gated,
> you cannot use DSP for noise squelch detection.   The application will tell
> you if there is sufficient squelch noise to utilize DSP noise squelch
> detection after you do the "radio tune rxnoise" command. If it fails, the
> audio type, amount, or quality isn't sufficient for DSP noise detection.
>
> When fed with good discriminator audio, the noise squelch detection in
> app_rpt is nearly as good as a Motorola M6709 (analog) squelch chip,
> commonly thought to be the high water mark in noise squelch detection.  999
> is the total absence of noise, and is the result one would expect with a
> full quieting signal, or an inappropriately muted RX audio line.
>
> Kevin W3KKC
>
>
>
> On 12/23/2018 7:28 PM, Brian G wrote:
>
> Hi all, Merry Christmas
>
> My local club is working on setting up a few ASL nodes, and I've been busy
> modifying some CM119 based USB sound cards to control the radios. I'm using
> this card/dongle:
> https://www.amazon.ca/Syba-SD-CM-UAUD-Adapter-C-Media-Chipset/dp/B001MSS6CS
>
> I've done several so far and have a few nodes working great with CTCSS
> carrier detect. One issue I'm consistently running into, is when setting
> the "RX Squelch Level" in the radio-tune-menu, it detects the current RX
> signal strength as 999. This results in the inability to use anything other
> than CTCSS for carrier detect. I can make plain old VOX work too, but it
> results in considerable (2 sec+) hang time.
>
> Using DSP carrier detect won't work because it's impossible to set the
> squelch high enough (max value 999). It always thinks there's a signal
> present when there isn't. This happens regardless of whether there's a
> radio connected to the dongle or not. As a matter of fact it happens even
> when plugging in an unmodified dongle right out of the package. I need it
> to work with no CTCSS. VOX would be fine if it wasn't for the hang time,
> but would rather use the DSP option in usbradio.conf.
>
> I assume it's just the nature of the beast, and if I want it done properly
> I need an adapter and radio capable of COS. But maybe someone knows if
> there's something that can be done or not?  Anyone have any insight on how
> to either eliminate the VOX hang time, or eliminate that "invisible"
> signal? I might be overlooking something. Thanks for reading!
> --
> Brian - VA3DXV
>
>
>
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